about $1/ft2 to the installed cost.
• Installing a white roof on a commercial
building yields annual energy savings
worth up to $0.20/ft2 and installing a
cool color roof on a home yields annual
energy savings worth up to $0.05/ft2.
Savings vary, and are greatest in hot
and warm climates. Use the DOE or
EPA calculator referred to later in this
document to estimate your savings.
• A cool roof may increase the need for
heating energy in winter by reflecting
sunlight that would otherwise warm
the building. However, winter penalties
can be smaller than summer savings
even in mixed climates (locations
with comparable heating and cooling
requirements).
How to Select and Buy Cool Roofing
Materials
The energy and cost savings that can be
achieved by using cool roofing technologies
depend on many factors, such as climate and
building characteristics.
Three aspects of cool roofing technologies
also affect their cost-effectiveness:
• The aged solar reflectance and thermal
emittance of the roof (since many roofs
become less reflective over time, energy
savings should be based on long-term
values of solar reflectance and thermal
emittance).
• The incremental initial cost of the cool
roof (if any).
• The incremental cost of keeping a cool
roof clean and reflective (if any).
Several tools are available to help consumers
and professionals choose appropriate cool
roofing materials and estimate their benefits.
• DOE’s Building Energy Software Tools
Directory provides information on 370
building software tools for evaluating
energy efficiency, renewable energy,
and sustainability in buildings.
http://apps1.eere.energy.gov/buildings/
tools_directory
• The DOE and the U.S. Environmental
Protection Agency (EPA) each offer
online calculators that estimate the
cooling energy savings and heating
energy penalties attained by installing a
cool roof.
DOE calculator:
http://www.ornl.gov/sci/roofs+walls/
facts/CoolCalcEnergy.htm
EPA calculator:
http://roofcalc.com
• The EPA lists thousands of ENERGY
STAR approved cool roofing materials.
http://www.energystar.gov/index.
cfm?c=roof_prods.pr_roof_products
• The Cool Roof Rating Council (CRRC)
maintains a program for measuring
and reporting the solar reflectances and
thermal emittances of roofing materials.
Their Rated Products Directory lists
over 1000 materials.
http://coolroofs.org
For more information, contact:
Marc LaFrance, DOE Technology
Development Manager for Cool Roofs
202-586-9142, [email protected]
Andre Desjarlais, Oak Ridge National
Laboratory Building Envelopes Group Leader
865-574-0022, [email protected]
Ronnen Levinson, Lawrence Berkeley
National Laboratory Heat Island Group,
510-486-7494, [email protected]
Cool roofs are ready to save energy, cool urban heat islands, and
help slow global warming.
Cool roofing is the fastest growing sector
of the building industry, as building owners
and facility managers realize the immediate
and long-term benefits of roofs that stay
cool in the sun. Studies exploring the
energy efficiency, cost-effectiveness, and
sustainability of cool roofs show that in
warm or hot climates, substituting a cool roof
for a conventional roof can:
• Reduce by up to 15% the annual airconditioning energy use of a singlestory building
• Cool interior spaces in buildings that
do not have air conditioning, making
occupants more comfortable
• Reduce carbon emissions by lowering
the need for fossil-fuel generated
electricity to run air conditioners
• Potentially slow global warming by
cooling the atmosphere
If you are installing a new roof or reroofing
an existing building, a systems approach to
providing an energy efficient roof should be
taken with a cool roof considered as one of
the options available.
A white roof saves energy by strongly reflecting sunlight
(high solar reflectance) and efficiently emitting thermal
radiation (high thermal emittance).
How Cool Roofs Work
Traditional dark-colored roofing materials
strongly absorb sunlight, making them
warm in the sun and heating the building.
White or special “cool color” roofs absorb
less sunlight, staying cooler in the sun and
transmitting less heat into the building. This
reduces the need for cooling energy if the
building is air conditioned, or lowers the
inside air temperature if the building is not
cooled.
The “coolness” of a roof is determined by
two properties and their combined effects on
temperature:
• Solar reflectance — the fraction of
sunlight that is reflected
• Thermal emittance — the efficiency
with which a surface cools itself by
emitting thermal radiation
Both properties are measured on a scale of 0
to 1 — the higher the values, the cooler the
roof.
The Emergence of Cool Roofs
Cool roofing is not a new concept. In the
mid-1980s, researchers at DOE national
laboratories in Tennessee and California
were measuring the energy-saving benefits
of “solar radiation control coatings” on
test roofs. Although energy savings were
confirmed in these early studies, they were
not sufficient to lead roofing designers and
installers to switch away from traditional
dark-colored roofing systems.
A parallel effort was launched to determine
the influence of light-colored roofing
products on summer urban heat islands.
This research demonstrated that solar
reflective roofs, solar reflective pavements,
and vegetation could lower urban air
temperatures, saving additional energy and
improving air quality.
Rolling blackouts during the summer of
2001 motivated California’s public utilities
to expand the scope of their peak load
management programs. They found that cool
roofing reduces peak demand for electricity,
helping to lower costs and avoid power
outages.
Twenty years after DOE initiated its work
on cool roofs, these products dominate the
commercial roofing marketplace in warm
and hot climates, partly because the State
of California changed its energy code to
prescribe cool roofing for most commercial
buildings with low-sloped roofs.
Today
Today both white and “cool color” products
are available for low-slope and steep-slope
roofs.
• Cool products are generally economical
on low-slope roofs for commercial or
industrial buildings.
• Cool options are available for most
traditional roofing materials.
• White roofs are coolest, but cool colors
are a popular alternative for roofs that
can be seen by neighbors.
• The U.S. EPA lists about 3,000
ENERGY STAR® compliant coolroofing materials.
• Federal tax credits are available for
some cool materials, including asphalt
shingles and metal products.
• Many state agencies and
utility programs offer
incentives for installing
cool roofs.
• Cool roof credits are
offered in sustainable
building programs such as
the U.S. Green Building
Council’s Leadership in
Energy and Environmental
Design (LEED).
Cool roofing for residential buildings need not be white; cool colors are
available for a number of roofing materials.
Cool Roofs Save Energy and Money in
Many Settings
Cool choices now exist for most traditional
roofing materials. Cool roofing should be
considered whenever construction or an
energy retrofit is being planned.
• For low-slope roofs (pitch ≤ 2:12), cool
thermoplastic membranes, elastomeric
coatings, and metal products are
available.
• For steep roofs, cool asphalt shingle,
clay tile, concrete tile, and metal
products are available.
Urban Heat Islands
(Adapted from EPA Urban Heat Island
Basics Compendium)
http://www.epa.gov/heatisland/resources/
pdf/BasicsCompendium.pdf
Air temperatures in many urban and
suburban areas are higher than those in
their rural surroundings; this regional
elevation in air temperature is called
an “urban heat island.” Many factors
contribute to urban heat islands. In rural
areas, trees and other vegetation provide
shade and also reduce air temperatures
by releasing water to the surrounding air.
Vegetative surfaces are also moderately
solar reflective. In contrast, urban areas
are characterized by dry and impervious
surfaces that strongly absorb light, such
as conventional roofs, sidewalks, roads,
and parking lots. As these urban surfaces
are warmed by the sun, they heat both the
interiors of buildings and the outside air.
Choosing solar-reflective roofing cools
the buildings and the outside air. Cool
roofs in an urban area can therefore:
• It is rarely economical to replace a
mechanically sound roof just to increase
its solar reflectance.
• Cool versions of some roofing materials,
including thermoplastic membranes,
coated metal products, and clay tiles are
available at little or no additional cost.
Cool asphalt shingles currently sell for
up to $0.50/ft2 more than conventional
asphalt shingles. Cool versions of
some other roofing materials, such
as modified bitumen, may require a
reflective surface coating that adds
• Lower the local air and ground
temperatures
• Improve human comfort and health
in uncooled buildings and outdoors
• Reduce the need for electricity to
cool buildings
• Decrease emissions of nitrogen
oxides (NOx), sulfur dioxide (SO2),
carbon dioxide (CO2), and/or
mercury (Hg) from electrical power
plants
Philadelphia, PA reduced temperatures in row houses
by installing cool roofs, which improves comfort
for occupants and may help reduce deaths from heat
waves. Baltimore, MD took similar steps following
the success in Philadelphia.